Fencing is required with SFCFS - this is because as multiple nodes write to the same disks, if you get split-brain, then corruption of the data is likely to quickly occur, where as with failover diskgroups, you have to import the diskgroup and mount the filesystem on the other node before any corruption could occur and there are mechnisms like pinging pubic IP which can prevent diskgroup importing.

You can use disk based I/O fencing which requires a minimum of 3 small disks (these must be separate from the data disks) or Server based fencing which requires a minimum of 3 Coordination Point servers (CPS) where CPS servers can be shared between many clusters.

I would say dIsk base fencing is better for you to configure as this just requires 3 disks as oppose to setting up 3 servers with CPS. You need 3 more very small LUNs in addition to your your 3 data LUNs - so Linux should see 6 disks (+ O/S disks), sdb, sdc etc. To set-up fencing you can use "/opt/VRTS/install/installsfcfsha<version> -fencing" - see "To set up disk-based I/O fencing using the installsfcfsha"section in SFCFS install guide.

I have never seen a minimum size given in the guides, but usually it is hard to produce small LUNs, so I think the smallest LUN I have used is 100MB. The default private region size I think is 64MB (maybe 32MB), so 100MB seems a sensible size.